Deformation Analysis of the Long-Period Stacking-Ordered Phase by Using Molecular Dynamics Simulations: Kink Deformation under Compression and Kink Boundary Migration under Tensile Strain

Abstract

The long-period stacking-ordered (LPSO) phase discovered in magnesium alloys is deformed upon the generation of a large number of unique deformation zones, which have no distinct orientation relationships at the deformation boundaries. These deformation zones are considered kink bands, but the mechanisms underlying their generation are not well understood. It has been suggested that the kink bands are responsible for the deformation of the LPSO phase, while simultaneously strengthening the material. In this study, the kink deformation process of the LPSO phase under compressive deformation was investigated through molecular dynamics (MD) simulations. The MD simulations showed that numerous prismatic ©aª dislocations were nucleated first, which led to cross-slips towards various basal planes and caused kink deformation. This was followed by the nucleation and motion of a large number of basal dislocations, as well as kink deformations in tandem with the formation of kink bands, which occurred through another process. In addition, the individual dislocations were indistinguishable at kink boundaries. In other words, sharp boundaries were formed. Next, a simulation was performed that applied tensile strain to the model after the compressive deformation described above was implemented on it. This revealed that while kink boundaries with large misorientation angles intermittently migrated because of the tensile strain, the kink bands were not easily removed.

In-Situ Observation on the Formation Behavior of the Deformation Kink Bands in Zn Single Crystal and LPSO Phase

“…37,38) As one of the suggested mechanisms, the local operation of pyramidal dislocation plays a role to induce the formation of pair of basal dislocations, and it leads to the development of deformation kink bands. In this case, since the motion of "one" pyramidal dislocation governs the formation behavior of the deformation kink band, the formation speed of the deformation kink band is expected to be much higher than that formed by the so-called "Hess-Barrett mechanism".…”

Influence of Volume Fraction of Long-Period Stacking Ordered Structure Phase on the Deformation Processes during Cyclic Deformation of Mg-Y-Zn Alloys

“…The strain is accommodated by <a>-slip and also by deformation of the LPSO phase. However, in tension, the kink formation is unlikely, and the LPSO phase is deformed rather by non-basal <a>-slip [40,41]. The enhanced dislocation activity both in the LPSO-phase and the magnesium matrix leads to high internal stresses and early failure of the material.…”

Electron backscatter diffraction pattern analysis of the deformation band formed in the Mg-based long-period stacking ordered phase

“…are still open questions. Recently, Matsumoto et al proposed a kink band formation model in which the operation of nonbasal slip (prism slip), which accompanied by cross-slip onto the basal plane, induces the generation of a densely packed edge-dislocation array perpendicular to the basal plane, from the results of a molecular dynamics simulation [31,32]. This model might explain the rapid formation of a kink band boundary observed in the LPSO phase [30], and its formation in the deformation when the load is applied parallel to the basal plane (i.e.…”